In these days, as the demand for portable electronic appliances such as laptop computers, video cameras, portable phones, etc., rapidly increases and the development of an electric vehicle, a storage battery for storing energy, a robot, a satellite, and the like hits its stride, active research has been conducted on high-performance secondary batteries capable of being repeatedly charged and discharged.
Secondary batteries commercially used at the present include nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, lithium secondary batteries or the like, among which the lithium secondary batteries are in the limelight due to their very low self-discharge rate, high energy density, and free charging/discharging since a memory effect does not substantially occur in comparison to nickel-based secondary batteries.
Such a lithium secondary battery mainly uses lithium-based oxide and a carbon material as a cathode active material and an anode active material, respectively. The lithium secondary battery includes an electrode assembly, which includes a cathode plate coated with the cathode active material, an anode plate coated with the anode active material, and a separator disposed therebetween, and an outer casing, i.e., a battery case, to accommodate with a hermetic seal the electrode assembly therein along with an electrolyte solution.
Generally, lithium secondary batteries may be classified, depending on a shape of a battery casing, into can shaped secondary batteries in which an electrode assembly is embedded in a metal casing and pouch-type secondary batteries in which an electrode assembly is embedded in a pouch of an aluminum laminate sheet.
Recently, secondary batteries have been widely used for medium and large devices such as vehicles or power storage devices as well as small devices such as portable electronic devices. For use in medium and large devices, a number of secondary batteries are electrically connected to increase capacity and output. Especially for medium and large devices, a pouch-type secondary battery is mostly used due to its easy accommodation and stacking.
A battery module may mean an element in which a plurality of secondary batteries are connected in series or parallel to increase capacity, output, etc. The battery module is electrically connected with external electronic devices by a power terminal. To this end, a conventional battery module includes a cartridge stack in which secondary batteries are accommodated, an interconnect board (“ICB”) housing including a first bus bar connected with an electrode lead of the secondary batteries, and a module case including a second bus bar connected with the first bus bar and a power terminal connected with the second bus bar.
Meanwhile, the first bus bar of the ICB housing is connected with the electrode lead of the secondary batteries and the second bus bar of the module case through laser welding. To this end, laser welding processing including two processes of a first welding process of laser-welding the electrode lead of the secondary batteries with the first bus bar after installation of the ICB housing and a second welding process of laser-welding the first bus bar with the second bus bar after installation of the module case. Thus, the conventional battery module has a complex electric connection structure between the secondary batteries and the power terminal, requiring much time in assembling the battery module.